So replay['stats']['0']['rank'] shows that the player with player index 0 placed 2nd.

As an aside, the engine actually keeps track of a number of other interesting stats for each player but unfortunately only rank gets saved to the replay. The other stats tracked are: last_frame_alive, init_response_time, average_frame_response_time, total_ship_count and damage_dealt.

Edit: Created a pull request to add the missing stats to the replay as PR #296